type foobar = (int , int) map

let empty_map : foobar = Map.empty

let map1 : foobar = Map.literal
  [ (144 , 23) ; (51 , 23) ; (42 , 23) ; (120 , 23) ; (421 , 23) ]
let map2 : foobar = Map [ (23 , 0) ; (42 , 0) ]

let set_ (n : int) (m : foobar) : foobar =
    Map.update 23 (Some n) m

let rm (m : foobar) : foobar = Map.remove 42 m

let size_ (m : foobar) : nat = Map.size m

let gf (m : foobar) : int = Map.find 23 m

let get (m : foobar) : int option = Map.find_opt 42 m
let get_ (m : foobar) : int option = Map.find_opt 42 m

let iter_op (m : foobar) : unit =
    let assert_eq = fun (i : int) (j : int) -> assert(i=j) in
    Map.iter m assert_eq

let map_op (m : foobar) : foobar =
    let increment = fun (i : int) (j : int) -> j+1 in
    Map.map m increment

let fold_op (m : foobar) : foobar =
    let aggregate = fun (i : int) (j : (int * int)) -> i + j.(0) + j.(1) in
    Map.fold m 10 aggregate